1. Field of the Invention
The present invention relates to a shutter control device and method for a camera.
2. Background of Related Art
Various shutter devices for cameras are known. One such device is a vertical movement type of focal plane shutter which includes front and rear curtains. Control of this type of shutter device is accomplished by causing the rear curtain to move with a predetermined time delay (i.e. a corrected shutter time) following the movement of the front curtain.
The corrected shutter time is obtained by adding a correction value to a determined shutter time. The determined shutter time is based on the set aperture amount, which is created between the two curtains, and the aperture time length (i.e. shutter speed). The correction value depends on the actual shutter action conditions and corresponds to an amount of time that the start movement of the rear curtain is shifted with respect to the front curtain. The correction values are stored in a memory. Correction is accomplished by causing the rear curtain to move at the corrected shutter time following movement of the front curtain. Specifically, the corrected shutter time is measured from the time the front curtain is moved to the open position.
However, with the above-described shutter control device, a problem arises when the shutter control is used with a shutter device having poor precision. Specifically, when there is a relatively long delay between either of the front or rear curtain control signals and actual movement of the respective curtain, the shutter curtains will not actually open for the appropriate shutter time, or even worse, they will not open at all. This problem is particularly significant as shutter speeds increase. Consequently, exposure of the film being is adversely affected.